Light sensitive silver halide photographic product for image transfer and process utilizing the same



1952 E. H. LAND ,584,030

LIGHT SENSITIVE SILVER HALIDE PHOTOGRAPHIC PRODUCT FOR IMAGE TRANSFER AND PROCESS UTILIZING THE SAME Filed Feb. 7, 1947 Base Layer) IO) {12 'Fhofosensirive Layer I ////x///// L\\\\ Soluble Subsfance of Acld Rcucflon FIG. 2

lNV NTOR Patented Jan. 29, 1952 LIGHT SENSITIVE SILVER HALIDE PHOTO- GR-APHIC PRODUCT FOR IMAGE TRANS- FER AND PROCESS UTILIZING THE SAME Edwin H. Land, Cambridge, Mass., assignor to Polaroid'Corporation,Cambridge, Mas's., a corporation of Delaware Application February 7, 1947, Serial No; 726,982

'This invention relates to photography, and to novel, photographic processes and products in general and is a continuation-in-part of my coending application Serial No. 662,000, filed April 13, 1948, for Photographic Product and Process. 5 forming components. This latter substance, in This invention relates more particularly to a preferred form of the invention, comprises a processes of the type wherein a positive image is silver halide solvent such as sodium thiosulfate. formed from a latent negative image in a silver With such a film of liquid composition between halide photosensitive layer by creatingpositive the exposed photosensitive layer and the imageimage-forming components under the selective carrying layer, the developer therein develops the control of the development of the latent image exposed silver halide and the silver halide soland by utilizing these image-forming compovent simultaneously forms soluble complex ions nents for creating the positive image. With such with the unexposed silver halide. These comprocesses, staining of the highlights of the posiplex ions are transported to the surface of the tive image is sometimes encountered due to the image-carrying l y Where y re Converted, existence of unused developer in stain-forming by means of the developer, to particles comcondition in said highlights. prisingsilver, these particles constituting a posi- It is a principal object of the present invention tive image of the latent negative image. to provide improved processes of the above type The creation of this layer of liquid, including whereby staining of the highlights of the posithe developer, is a mechanical process and subtive image is prevented and a stable positive ject to considerable variation as the result of difimage is obtained which requires no washing. ferent conditions of temperature, etc., during the Still another object of the present'invention is spreading of the liquid. Therefore, it is desirto provide novel composite photographic film able, in some cases, to include in the layer of liqunits and products particularly suitable for .use uid composition more developer per unit area with such processes. than would ordinarily be required to fully cover These and other objects of the invention will and develop the negative image. Some of the in part be obvious and will in part appear hereexcess developer may remain on the image-carinafter. rying layer containing the positive image.

The invellfiml accordingly Comprises epf It has been found that this excess developer, u t p s n t e features, pr p and h particularly in the highlights of the positive imrelation of components, and the. process involvn be nd red incapable of stainin the ins th s ver l eps nd he relation and h positive image if the alkalinity of this positive Order Of 0116 more Of u t ps h respect image is lowered, neutralized, or slightly acidified. to each of the others which are exemplified in i is accomplished, in a preferred form. of the the following detailed disclosure, and the scope ti by including on the image-carrying Of the application (if which W11] be indicated in laye a, substance which slowly react with the the Clalmsliquid composition and slowly lowers the pH of For a fuller understanding of the nature and t liquid composition, for example to pH of objects or" the invention reference should be had: 7 6 or lower, If the develgper i t is t to' the following detailed description; taken in rapidly acidified by t t i on t image. conneflltlon 71th the acmmpanyjng drawing carrying layer, it may adversely affect-the abilwhefrelm ity of the developer to develop a strong nega- Figure 1 IS an exaggerated cross-sectional view tive. and ,1 a t pesmve image Th refore 0f El pre red Composite photographic fi the acidification step is so adjusted that the lowembodying me present invention; and eringof the pH is not accomplished, at least to Fig. 2 is an exaggerated cross-sectional view any substantial degree, until after the positiv of another composite ph t raphic film unit emimage has been formed. However, it does take y g the present invention. place quite rapidly after the positive image has In the photographic processes with which this been formed. invention is particularly involved, a sheet of pho- One preferred method of obtaining acidiflca tosensitive material, preferably a silverhalide, is tion of at least the highlight portions of the posiexposed to aotinic light to create therein a lat-- tive image is to utilize a salt on the image carryent negative image. Ihis latent image is deing layer which is slowly dissolved by the liquid veloped and a positive image' thereof is formed composition, andwhich slowly'foims insoluble 45 Claims. (CI. --8) on an image-carrying layer, preferably by creating between the two layers a uniform film of a viscous alkaline developer solution containing a substance capable of forming positive imagecompounds with the alkali used to make the developer composition highly alkaline. In one preferred form of this modification of the invention, the alkali used in the liquid composition is sodium hydroxide and the material on the imagecarrying layer is a metallic salt which, when dissolved in the liquid composition, slowly forms insoluble metallic hydroxides with the hydroxyl ions in the liquid composition. As the metallic hydroxides precipitate out of the solution they lower the pH thereof to about 5 or 6.

In general, the prevention of stain caused by excess developer in the positive image may be accomplished if the salt, used for preventing the stain, be one which, only slowly lowers the pH of the solution so as not to interfere with the development of the positive and negative images. It is desirable that the salt, whendissolved,-be one which, in the concentrations used, does not appreciably destroy the latent negative imageor at least does not have any such effect before the development of the latent image, in view of the rapid development of the negative. The

salt should also be capable of combining slowly with hydroxyl ions in the liquid composition to precipitate these ions as insoluble or only slightly soluble hydroxides, these hydroxides being preferably white, or colorless, and stable, or having white or colorless end products. It is also desirable that any unreacted portions of the salt be white or colorless and relatively stable.

While many metallic salts satisfy the requirement of the formation of the relatively insoluble metal hydroxide, it is preferred that those metallic salts be used which do not decompose upon dissolution in water. Of these latter metal salts the acetates and nitrates are preferred. Preferred metal salts are the acetates and nitrates of lead, zinc, nickel and cadmium. Another preferred method 'of obtaining acidification of at least the highlight portions of the positive image is to utilize, on the image-carrying layer, an acid or acid ester. This acid may be of the type which is slowly dissolved by the liquid composition and slowly lowers the pH thereof or it may be of the type which would ordinarily be rapidly dissolved, but is protected from rapid dissolution by positioning a slowly permeable layer between the locus of the acid and the liquid composition. In some cases the slowly permeable layer may itself be an acid or acid ester.

One preferred type of acid or acid ester is a high polymer having free carboxy or phenolic hydroxy groups along the chain. Preferred polymers of this type are modified cellulosic derivatives containing free carboxy groups along the chain, for example, a cellulosic acid, such as carboxymethyl cellulose, or a cellulosic acid ester, such as cellulose acetate hydrogen phthalate. These polymeric substances have a very low mobility in solution and ordinarily do not need to be protected from the liquid composition.

I When the more soluble inorganic or lower molecular weight organic acids are utilized such, for example, as citric acid, they are preferably covered by a slowly permeable layer, for example, a slowly permeable high polymer which, in turn, may comprise one of the above-mentioned high polymers. When a solid acid, such as palmitic acid, is employed, it can, in somecases, be used without any protective coating.

Referring now to Fig. 1 there is shown a com-, posite photographic film unit which embodies 'to carry, on one surface thereof, a photosensitive layer I2. There is also provided an imagecarrying layer 14, which is adapted to carry on its surface the final positive image. Between the image-carrying layer l4 and the photosensitive layer I2 there is" positioned a container l6 adapted to have therein a liquid composition. This container can be attached to either the photosensitive layer I2 or the image-carrying :layer M or can be separate from either of these layers.

The base layer I0 is preferably made of a suitable film base material such as a cellulosic ester or mixed ester, such as cellulose nitrate, cellulose acetate,' cellulose acetate propionate, or other substance capable of supporting a photosensitive emulsion. This base can be made opaque, if desired, by addition of suitable dyes or pigments to the above-named substances or the base can be made of paper and other materials suitable for carrying a photosensitive emulsion. The photosensitive layer I2 is preferably of the type rendered developable by exposure to light, e. g.. an emulsion of a noble'metal halide, and in particular, an emulsion of a silver halide or of a mixture of silver halides, or of a mixed silver halide.

The image-carrying layer l 4 in a preferred embodiment comprises a sheet of paper known in the art as baryta paper. The inner surface of this image-carrying layer, i. e., the surface nearest the photosensitive layer, is prepared, in one modification of the invention, in the following manner:

Example 1 A continuous strip of baryta paper is run through a bath comprising a water solution of 30% lead nitrate and 10% zinc nitrate, the speed being such that the baryta paper is in the bath for about one minute.

The image-carrying layer l4 may also be formed of many other materials. This layer is preferably permeable to a substance contained in the liquid composition, although this permeability is not required, particularly if there is a permeable coating applied to the surface thereof. The image-carrying layer I4 may also be made of gelatin, regenerated cellulose, polyhydroxy alkanes, such for instance as polyvinyl alcohol, sodium alginate, certain of the cellulose ethers such as methyl cellulose and their derivatives such as sodium carboxy-methyl cellulose or hydroxyethyl cellulose, carbohydrates such as gum or starch and mixtures of these materials where the latter are compatible.

7 The liquid composition in the container 16, in its preferred embodiment, comprises a developer such as hydroquinone and a film-forming substance such as sodium carboxymethyl cellulose which acts to form a dimensionally stable imagereceiving layer when spread between layers l2 and I4. There is also included a substance adapted to form positive image-forming components from a latent negative image. This latter substance, in a preferred form of the invention, is a silver halide solvent such as sodium thiosulfate. There are also preferably included other substances to aid in the photographic .reaction, such as a preservative, i..e., sodium sulfite,

and an alkali, i.-e., sodium hydroxide, plus water, to carry the above-mentioned elements in solution. A suitable liquid-composition may .be prepared by dissolving the materials shown in the following nonlimiting example:

Example? Grams Water 1860 Sodium carboxymethyl cellulose 93 Sodium sulfite '78 Sodium hydroxide 7416 Sodium thiosulfate 14.5 Citric acid 38.5 Hydrcquinone -d 52.0

' impervious material such, for example, as a sheet of wax-impregnated metal-coated paper, waxcoated metal foil, or a metal foil coated with a resin, such as polyvinyl butyral, which is inert to alkalies.

In the use of the 'film unit of Fig. 1 the photosensitive layer 12 is :exposed toa subject image by light passing through the base layer 10. The

processing of the film unit is next preferably accomplished by applying a mechanical stress to the film unit for the purpose of releasing the liquid composition from the container I6 and spreading it ina uniform thin layer between the image-carrying layer l4 and'the photosensitive layer 12. Such processing can be most readily accomplished by passing the film unit through a pair of pressure rollers, the container end of the film unit passing through the rollers first. When the liquid composition is spread between the photosensitive layer l2 and the image-carrying layer [4, the developer develops the latent photographic image and the sodium thiosulfate simultaneously forms soluble silver complexes with the unexposed silver halide grains. These soluble silver complexes are transferred to theimage-carrying layer and the layer created by the film-forming sodium carboxymethyl cellulose in the liquid composition where they are converted into insoluble visible particles constituting the positive image on the surface of the image-carrying layer as well as within the layer of sodium carboxymethyl cellulose.

While the above reactions are taking place, the lead nitrate and zinc nitrate are slowly dissolved by the liquid composition and release free lead, zinc and nitrate ions to the liquid composition. The decrease of alkalinity is primarily effected by the lead and zinc ions which slowly form relatively insolublehydroxides, slowly crystalli-zing and precipitating these insoluble hydroxides from solution. Thisreaction progresses at a rate sufficiently slow to permit'the positive image .to be,-formed.in :an alkalinesolution, and

sufllciently fast-so that :the ofrthe solution is lowered to a neutral or slightly :acid condition within ashorttime.

In another method of preparing an imagecarrying layer of .the present invention the .following steps are followed:

Example? vA continuous strip :of .baryta paper is run through a :coating :bathcomprising a 3 water solution of lead acetate, the speed :of movement being such that thebaryta paper .is in the bath for about thirtyseconds. The sheet isdried and then run through a bath comprising 2, water solution 50f sodium sulfide, the speed being such that the :baryta paper .is in the bath for about :fifteen seconds. It appears that the image-carrying layer iprepared in the above manner contains lead sulfide andrsome lead ace tate with no sodium zsulfide'assuch. Thesheet is then treated-in accordance :with thezprocess of Example 1. The second .bath,.in addition to'supa plying zinc and lead salts to the-sheet, alsohas the efiect of dissolving thesmallest le.ad:sulfide grains. When such rasheet is used withaliquid composition of the type described in Example 2, the alkaline liquid composition slowly releases free sulfide ions from the coating of the imagecarrying layer M, which accelerate :the positive image-forming reaction andzincrease the density, contrast and gamma of the positive image, particularly where the photosensitive layer contains a relatively high percentage of silveriodide.

In still other methods of preparing image- .carrying layers in accordance with the present invention'the followingbaths maybe used:

Example 4 A water solution containing :by weight ..5% cadmium acetate, 10% :lead :acetate, and 50% zinc nitrate.

Emample 5 A solution containing .byweight 10% cadmium acetate, 30% lead acetate, and 30% zinc nitrate.

.Eccampleo A solution containing by weight 50%i zinc nitrate.

Example? A water solution containingsby weight 30% of manganous acetate.

Example 8 A water solution =,containing by weight 1% lead acetate, 10% cadmium.acetate-and.30% zinc nitrate.

The .solutionsgiven in the above examples are subject to considerable variation. As a general proposition it may be stated that, when a developer solution of "the type described :in Example 2 is used, i. e., one having a pH of about 11 or above, the image-carrying layer should be treated in the bathsof Examples 1 and 4 through 8 for approximately .15 to 30 :seconds. When the alkalinity of the developer solution is decreased, the timerof dippingxof theimage-carrying layer in the above .Jbathsmay'be decreased. When the concentration of'the'bath is decreased, the time of dipping should be increased. The permability of the image-carrying layer may also affect the time of dipping. As an example, with single-weight barytapaper procured "from Eastman Kodak Company, .the timeyo'f 'idipping or 1y be'-increased. vFor double-weight baryta, the time of dipping and concentrations should be as above. This difference appears to be due to the possibility that single-weight baryta is more impermeable than thedouble-weight baryta to solutions of these materials.

In the above solutionathe acetates and the nitrates of the various metal salts may generally be used. interchangeably. The nitrates, be-

ing salts of-a stronger'acid, may usually be employed in slightly smaller quantities than the acetates. With highly alkaline developer so;- lutions of the typeset forth in Example 2, and with dipping times of between 15 seconds and one minute, the total weight of the lead and/or zinc salts in the bath should be in the neighborhood of 30% or more to get complete neutralization of the bath of Example 8 is particularly adapted for use in photocopy work where the photosensitive layer comprises a contrasty negative .such as that sold byEastman Kodak under the trade name ofKodabromide 4025 and the imagecarrying layer comprises a sheet of ordinary bond paper. 1

In still another method of providing the metallic salt on the image-carrying layer there is provided a film unit of the type shown in Fig. 2, where like numbers correspond to like elements of Fig. 1. In this case the salt, is absorbed by the image-carrying layer M of Fig. 2 and then covered by a coating: I8 of a film-forming material. Such a method is set forth in the following nonlimiting example:

Example 9 A sheet of single-weight baryta paper is run through a 50% water solution of lead acetate, being in contact with the solution for about 1 minute. The sheet is then dried and there is applied to the surface thereof a coating 18 approximately .015 inch thick of a water solution of sodium carboxymethyl cellulose. With such a coating technique, the lead partially insolubilizes the sodium carboxymethyl cellulose, by cross-linking therewith, and thus increases its insolubility. The lead sodium carboxymethyl cellulose, due to its increased insolubility, seems to slow down the dissolution of the lead ions. Thus, this type of. image-carrying layer may be used in processes where high concentrations of water-soluble lead salts might otherwise be undesirable due for example to their possible effect of decreasing the gamma of the positive image, with some emulsions.

In the use of the modification of the invention of Fig. 2, the metallic salt, or salts, are slowly released from the image-carrying layer l4 and serve the same function as previously described, the permeability of coating I8 controlling the speed of dissolution of the salt or salts from layer. l4.

The above description of the invention is concerned with preferred modifications and is subject to considerable variation without departing from the scope thereof. For-example, the metallicsalt, or saltsused for forming therelatively insoluble metallic hydroxide maybe applied to the image-carrying layer in a number of ways other than by dipping the image-carrying layer in a water solution thereof. As an example of such a modification of the invention, the salt, or salts, may be incorporated in solid or dissolved form in a' suitable film-forming material and then coated on the image-carrying layer.

When an acid or acid ester is used on the image-carrying layer, a preferred type is a high polymer, as mentioned previously. A particular advantage of this type of acid resides in its relative immobility and its enteric solubility characteristics, 1. e., its insolubility in an acid solution and its solubility in an alkaline solution. These characteristics make thissubstance particularly useful where the polymeric acid or acid ester is used as a base coat on the imagecarrying layer, on top of which there is placed a coating of a colloidal precipitant, such as, lead sulfide. When the colloidal precipitant is coated over the polymer it is preferably applied in a slightly acid or neutral medium. Thus it does not appreciably dissolve the undercoat of the polymer. During the processing reaction, the alkalinity of the liquid composition is slowly lowered by the polymer as the hydroxyl ions diffuse down to the relatively immobile polymer, thus causing neutralization.

Several preferred types of polymeric acid sub stances may be incorporated on the surface of the image-carrying layer, for example, by providing a coating i8 thereof in a modification oi the invention of the type shownin Fig. 2. This type of coating may be formed as described in the following nonlimiting examples:

Earample 10 A baryta image-carrying layer is coated with a thin layer of a 5% water'solution of sodium carboxymethyl cellulose. This coating is then converted to the acid polymer, carboxymethyl cellulose, by dipping for 1 minute in a 15% water solution of hydrochloric acid, followed by a washing in plain water. This acid polymer can also be prepared by adding an acid, such as citric, to the water solution of the sodium salt of the polymer.

Example 11 V A solution containing 20 grams of cellulose .acetate hydrogen phthalate dissolved in 50 cc. of acetone is doctored, or roll-coated, on a baryta image-carrying layer. This is next preferably covered with a dispersion of lead sulfide and silica aerogel in water.

Other acid cellulose derivatives that maybe used are cellulose hydrogen phthalate, carboxyethyl cellulose, and. carboxy cellulose. Equally, other acid polymers, such as polymethacrylic acid, may be used.

When readily soluble inorganic or readily soiuble low molecular weight organic acids are employed, it is desirable to slow down the dissolution of these acids by the liquid composition. This is preferably accomplished by the formation of a slowly permeable layer over the acid which has been imbibed onto the surface of the imagecarrying layer. It is possible, however, to include such an acid in solid or dissolved form in a film-forming material which is slowly permeable, or to coat the acid on the back of the image-carrying layer, i. e., that side thereof which is farthest from the photosensitive layer. When solid acids are used, particularly those Jwhicha'reonly slowly soluble in an alkaline soluthey would be if layer.

ItIis generally preferred to; utilize-such acids under; or' in; a; protective medium which'slowsf down their rate of dissolution so. that, even mesa-03o 9 tion; they can be used: without any protective. coating. Various specific methods of incorporating an acid in. film units of the type shown par ticularly in Figs. 1. and 2. above-are set forth in the following, nonlimiting examples:

Example. 12

2 grams of diphenyl disulfonic acid are added to 30 grams of a 2% water solution of sodium carboxymethyl cellulose andspreadl on a baryta image-carrying layer.

Example 13 2 grams ofisuccinic acid are added to 30 grams of a 2% water solution of sodiumcarboxymethyl cellulose and coated on a barytaimage-carrying. layer. Over this coating there is. applied another coating, of'a water solution of sodiumcarboxymethyl cellulose.

Example 14" 1 /2.grams of malic acid are. added to 30 grams of. a 2% water solution of. sodiumcarboxymethyl. cellulose and coated. on abarytadmage-carrying.

layer.

Ezrample lfl 1 grams of O-phthalic acid dissolved in methanol are added to 30' grams of'a 2% water solution of sodium carboxymethyl cellulose and coated on a baryta image-carrying layer.-

Erample 16:

520%" water solution of maleic' acid is" painted on the back of asingle-weight baryta image-- carrying layer.

Eammplel? A,5 water. solution of. palmiticiacidis. painted on: the. back. of a single-weightharytaimagecarrying layer.

Example 18 5 grams of molybdic acid are added to 15 cc. of a 10%. water solution of sodium hydroxide. The image-carrying layer is dipped in this solution for 5 minutes and dried. Then it is dipped in a 5% hydrochloric acid solution to obtain molybdic acid and sodium chloride.

Example 19 A 5% solution of salicylic acid in water and methanol is applied to a baryta image-carrying layer by dipping for about 5 minutes.

Other solid acids that maybe applied to the image-carrying layer by imbibing from water, or other solutions thereof, are as" follows: oxalic acid, sebacic acid, hydrocinnamic'acid, metanilic acid, palmitic acid, paratoluene sulfonic acid, and

benzenedisulfonic acid. These acidsfmay be added in solutions of organic solvents, or water,

material, depending upon and a film-forming their solubility.

With respect to the acids" which are included in, on, or under the image-carrying layer it may be stated generally that their concentration should'he'adjustedto their solubility and the per-'- meability'of' any protecting'medium in which, or

under: which, theyarelocated'. Thus'when the v acids are coated on thefront of 'theimage-carry though a great cxcess'ofl acid'maybe presenti the acid does not lower the pH of the: developer solution to any substantial degree until the imageforming reaction is complete.

The invention described above may be considerably modified such as byc'ombining certain of the above treatments, for example by using an acidpolymer layerrof the type" described in Example 11 over a metallic salt layer of the type described in Example 5, or an acid layer'of the type described in Example 12.

While the acidifying substance is preferablyineluded on or associated with the. image-carrying: layer, this is not essential and'it might, for" ex'- ample, be positioned between the photosensitive layer and the base carrying this photosensitivelayer, or on the backside of the base for the photosensitive: layer, in thosecases. where this ,base is at least slowly permeable to the liquid composition. It is preferred, however, that this acidifying substance, whether acid, polymer or salt, be associated with the image-carrying layer,

since in most cases it is desirable to be able toseparate the positive image from the negative image. at a predetermined timeduring the p rocessing thereof. It is alsodesirab'le in most cases 'tohavethe acidificationor neutralization of the positive image take place after. thepositive image has been. completely formed. Thus: when:

the acid substance is. associated with the image-- carrying layer, this. layer, having on its surface the positive image, maybe separated from the negative photosensitive layer at any predetermined time and the acidification or neutralization of the positiveiimage may continue after this positive image has been. separated" from the photosensitive layer.

With the-use of substances of acid reaction on the image-carrying layer, some quite remarkable: conditionsare encountered. This is particularly true when the substance is an acid salt sincethepH of the layer of liquid, amomentafter spread-- ing, seems to be much lower. atthesurface of the image-carrying layer thantat-the surface of the photosensitive layer. As. permeation oithetwo layers continues the pH of the liquidlayer reaches 1 a value which is lower than the pH of. the-liquid initially but which may be higher (particularly in the shadows) than the initialpH of the liquid at the surface of the image-carrying layer when it first contacted the image-carrying layer. This variation of. pH through the depth of thelayer may be used in some casesto. aid inpreventing the initial precipitation-of silver in the positive image, thereby giving a momentary time: delay ili ing'layerthey must, unless relatively slowly solv uble, be incorporated in smaller quantities than protected'by a slowly permeable between development of. the. negative and positive images, which is. sometimesof assistancei 1 maintaining clear highlights. It is also contemplatedby the presentsinventionthat the above processesof. acidification of the positive image may. becarried-out bydipping. the. imageecarrying layer, having thereon. the.

final positive image, in.abathcontaininga-solution of an acid salt.

specification and the attached claims represents In certain industrialap plications it is possible to. acidifyor neutralizeitlie liquid to said element is effective to give a finishedprint sufliciently'stable to require no subsequent liquid stabilizing treatments, which process comprises the steps of bringing a relatively uniform layerwise distribution of a processing liquid into contact with the photosensitive element so as to permeate said emulsion with said liquid, said layerwise distribution of processing liquid providing the entire mass of liquid for performing said process; providing a print-receiving element in superposed relation with the photosensitive element, said print-receiving element being at least partially permeable to the processing liquid and the layerwise distribution of the processing liquid being confined between the outer surfaces of said superposed elements throughout the processing, said processing liquid containing, afterpermeation of said silver halide layer, all of the reagents, including a silver halide developer'and an alkali, for developing the latent image in the silver halide emulsion and for forming a positive print of the subject matter of said latent image upon said print-receiving element, said developer being characterized by its propensity for oxidizing in an alkaline environment to form stains; and introducing into the alkaline processing liquid, subsequent to its contact with i the photosensitive element, a substance of acid reaction in suificient concentration to reduce the alkalinity of said processing liquid to a pH at which the unused developer therein is substantially incapable of oxidation to form a stain in said positive print, said substance of acid reaction being dissolved from a permeated portion of one of said elements and being present in said processing liquid in addition to all of the reagents forforming the transfer print.

2. The process of claim 1 wherein the liquid is spread in a layer between the photosensitive element and the print-receiving element.

3. The process of claim 2 wherein the liquid as spread contains, in solution, the alkali and the devzloper, and also contains a silver halide solven I 4. The process of claim 1 wherein the substance of acidreaction comprises at least one neutralizing metal salt carried adjacent the inner surface of one of said elements, said neutralizing metal salt being soluble in the processing liquid and the metal ions thereof forming a metallic hydroxide which is substantially more insoluble in the processing liquid than is said neutralizing metal salt. 7

5. The process of claim 1 wherein the substance of acid reaction comprises a plurality of neutralizing metal salts carried adjacent the in- V ner surface of one of said elements, said neuessing liquid and the metal ions thereof forming 1-2 insoluble in the processing liquid than are said neutralizing metal salts.

6. The process of claim 1 wherein the substance of acid reaction is an acidic high polymer located adjacent ,theinner surface of said printreceiving element.

'7. The process of claim 6 wherein the acidic high polymer is a cellulosic compound and has free carboxy groups along its chain.

8. The process of claim -.1 wherein the substance of acid reaction is provided by the printreceiving element and comprises an acid located beneath the inner surface of the print-receiving element, said acid being overlaid with a layer of solid material slowly permeable to the processing liquid. 1

9. The process of claim 1 wherein the substance of acidreaction is an acid dispersed depthwise throughout at least a substantial'portion of the thickness of the print-receiving element. 7

10. A photographic process for forming, by transfer, a positive print of a latent image contained in thesilver halide emulsion of a photosensitive element wherein a single application of liquid to said element is effective to give a finished print sufficiently stable to require no subsequent stabilizing treatments, which process comprises the steps of spreading, in a layer between the photosensitive element and a printreceiving element, all of the processing liquid for performing said process, which liquid includes, in: solutiona silver halide developer, a silver halide solvent and an alkali and which, when spread, permeates the silver halide emulsion, said liquid developing a latent image in said emulsion and forming a positive print in silver upon said print-receiving element, the developer being characterized by its propensity for oxidizing in an alkaline environment to produce stains; after formation of the positive print, separating said print-receiving element from said photosensitive element; and at some stage of the proc ess, subsequent to the spreading of the liquid, in-' troducing into the processing liquid a substance of acid reaction, by dissolving the same from said print-receiving element, said substance being carried in solid form by said print-receiving element in a sufficient amount to reduce the alkalinity of the processing liquid of said print-receiving element to a pH at which the unused developer in said liquid is substantially incapable of oxidation to form a stain in said positive print;

11. The process of claim 10 wherein the, substance of acid reaction com rises at least one neutralizing metal salt carried adjacent the inner surface of said print-receiving element, said neutralizin metal salt being soluble in the proc: essin liquid and themetal ions thereof forming a metallic hydroxide which is substantially more insoluble in the processing liquid than is said neutralizing metal salt.

12; The process of claim 10 wherein the substance of acid reaction comprises at least one neutralizing metal acetate carried adjacent the 'inner surface of one of said elements, said neutralizing metal acetate being soluble in the processing liquid and the metal ions, thereof forminga metal hydroxide which is substantially more neutralizing metal acetate.

13. The process of claim 10 wherein the sub-' stance of acid reaction comprises zinc acetate and is carried adjacent the inner surface of said" tate and. iscarried. adjacent the innensurface of said print-receivingv element.

15.. The. process of, claim, whereinthesub tralizing metal nitrate being soluble in the processing liquid and the metal ions thereof forming a metallic hydroxide which is substantially more insoluble in the processing liquid than is saidneutralizing metal nitrate.

16. The process of claim 10 wherein theisub,- stance of acid reaction comprisesa plurality of neutralizingmetal salts carried. adjacent the in ner surface: of one of said print-receiving ele-- ments, said? neutralizing metal salts'being soluble in the processing liquid and the metal ions there;- of' forming metallic hydroxides which are substantially more'insoluble in the processing liquid than are said neutralizing metal salts.

1.7. The process of claim 16 wherein the said neutralizing salts are a mixture of lead; cadmium and zinc salts.

18. The process of claim 10 wherein the substance of acid reaction is an acidic cellulosic high polymer having free carboxy groups along" its chain and is located adjacent the inner surface of said print-receiving element.

19. The process of claim 10 wherein the substance of acid reaction is a layer of carboxymethyl cellulose and is located adjacent thein ner surface of said print-receiving element.

20.- Theprocessof claim 10 wherein the substance of acid reaction is a layer of cellulose acetate hydrogen phthalate and is located adjacent the inner surface of said print-receiving element.

21. The process of claim 10 wherein the substance of acid reaction is an acid, substantially all of which is located beneath the surface of said print-receiving element so as to be only slowly accessible to the processing liquidspread over said print receiving-element.

22. The process of claim 10 wherein the substance of" acid reaction is a palmitic acid, substantially all of which is located beneath the surface of said print-receiving element so as to be only slowly accessible to the processing liquid spread over said print-receiving element.

23-. The process of claim 10 wherein the sub stance of acidreaction is amaleicacidsubstan tiallyall ofwhich is located beneaththe surface of said print-receiving element so as tobe only slowly accessible to. the processing liquid,- spread over said print-receiving element.

24. A photographic product comprising a liq uid-confining layer, including at least a photosensitive portion, said photosensitive portion com:-

prising silver halide as the photosensitive: ma.-

terial thereof, another liquid-confining layer and a rupturable container holding a liquid, said layers and said container being associated together so as to permit said layers to be superposed with said liquid held by said container so as not to wet said layers and with said container positioned for releasing said liquid between said layers, said product containing all of the reagents, including a silver halide developer and an alkali, in sufiicient quantity to develop a latent image in said photosensitive portion and to provide a layer of said product, other than said photosensitive layer, with a positive transfer print of the subject matter of said latent image, said reagentsbeing: rendered effective upon" the: release oii'saidzliquid fromthe rupturable container, said silver halide developer tending to. oxidize and io m'stains in an alkalineenvironment, said productcontaining, invaddition to all of said reagents for forming. a' transfer print, a substance of: acit reaction which is' earried by oneof the; layers of said product in a position tobe dissolved in said liquid upon the release thereof, said substance of acid reaction: being operative to reduce the alkalinity of the liquid at a rate substantially slower than the rate at which the developing reaction takes place and being'suflicient'inquam tit-y' to reduce thev alkalinity of the processing liquid to a pH at which" the developer is substantialiy incapable of oxidizing to form stains in said. positive transfer print,

25. The product of claim 24 wherein the container is mounted so as to spread its contents in a layer between'the photosensitive layer and the print-receiving layer.

26. The product of c1aim25 whereinthe liquid in thecontainercontains, in solution, the alkali and' the developer, and also: contains a silver halidesolvent;

27. The product of claim 24 wherein the substance of acid reaction comprises at least one neutralizing metal salt, said neutralizing metal salt being soluble in the processing liquid and the metal ions thereof forming a'metallic hydroxide which is substantially more-insoluble in the processing-liquid than is said neutralizing metal salt.

28.: The: product of claim 24" wherein the substance of acid reaction comprises a plurality of neutralizing metal salts, said neutralizing metal salts being soluble in the processing} liquid and the metal ions thereof forming metallic hydroxides which are substantially more insoluble inthe processing liquid than are said neutralizing metal salts.

29; The product of claim 24 wherein the substance of acid reaction: is a filrnof' an acidic high polymer located adjacent'the inner the print-receiving layer.

30. The product of claim 29 wherein the acidic high polymer is a cellulosic compound and has free carboxy groups along its chain.

31. The product of 'claim'24 wherein the sub stance of acid reaction is'anacid, substantially all of which is located beneath the surface of one of said layers between which the liquid is released so as to be only slowly accessible to said liquid.

surface of 32; A photographic productfcapableof formingtransfer prints in "conjunction with a photosensitivesilver "halide ielement, said product com-1' prising a rupturable containing nieansholding a-liquid, and a sheet support upon which said containingmeansis mounted, said sheet support providing an imageereceiving area-adjacent said containing means and onto which said liquid is spreadable in a thin layer directly from said containing means, said product carrying all of the reagents, including a stain-forming silver halide developer and an alkali, for forming a transfer print of a latent image in a silver halide emulsion, said reagents and said liquid being sufllcient in amount and being so located in relation to said image-receiving area that the spreading of said liquid over said area disperses the silver halide developer and the other reagents throughout said area in adequate quantity to form a transfer print of a latent image in an area of a contiguous silver halide element equivalent to said image-receiizing area, said support carry-.

ing, distributed over said image-receiving layer and in addition tosaid reagents, a substance of acid reaction in 'suflicient quantity to substantially neutralize said liquid when spread on said support from said containing means, said substance consuming alkali at a substantially slower rate than the rate at which said reagents form a transfer print.

33. The product of claim 32 wherein the liquid in the containing means contains, in solution, the alkali and the developer, and also contains a silver halide solvent.

34. The product of claim 32 wherein the substance of acid reaction comprises at least one neutralizing metal salt carried adjacent the surface of said support upon which said liquid is spread, said neutralizing metal salt being soluble in the processing liquid and the metal ions thereof forming a metallic hydroxide which is substantially more insoluble in the processing liquid than issaid neutralizing metal salt.

35. The product of claim 32 wherein the substance of acid reaction comprises a plurality of neutralizing metal salts carried adjacent the surface of said support upon which said liquid is spread, said neutralizing metal salts being soluble in the processing liquid and the metal ions thereof forming metallic hydroxides which are substantially more insoluble in the processing liquid than are said neutralizing metal salts.

' 36. The product of claim 32 wherein the substance of acid reaction is an acidic high polymer located adjacent the surface of said support upon which said liquid is spread.

37. The product of claim 36 wherein the acidic high polymer is a cellulosic compound and has free carboxy groups along its chain.

38. The product of claim 32 wherein the substance of acid reaction is an acid, substantially all of which is located beneath the surface of the support on which the liquid is spread so as to be only slowly accessible to said liquid.

metal n1trate carried ad acent the surface of ,McGra W Hm copyright 1939 said support upon which said liquid is spread, said neutralizing metal nitrate being soluble in the processing liquid and the metal ions thereof forming a metallic hydroxidewhich is substantially more insoluble in the processing liquid than is said neutralizing metal nitrate.

41. The product Of claim '32 wherein the substance of acid reaction comprises a plurality of neutralizing metal salts carried adjacent the surface of said support upon which said liquid is spread, said metal salts including salts of cadmium, zinc and lead, and being soluble in the processing liquid, the metal ions of said salts forming metallic hydroxides which are substantially more insoluble in the processing liquid than are said neutralizing metal salts.

42. Theproduct of claim 32 wherein the substance of acid reaction is cadmium acetate.

43. The product of claim 32 wherein the substance of acid reaction is zinc acetate.

44. The product of claim 32 wherein the substance of acid reaction is a layer of carboxymethyl cellulose and is located adjacent the sur-.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENT Number Name Date 742,405 Eichengrun Oct. 27, 1903 1,841,653 Van der Grinten Jan. 19, 1932 1,928,192 Walker Sept. 26, 1933 1,930,140 Becker Oct. 10, 1933 1,956,230 Schmidt Apr. 24, 1934 2,315,966 Knott Apr. 6, 1943 2,352,014 Rott June 20, 1944 2,366,439 Chilton et a1. Jan. 2, 1945 2,393,583 Balassa et al. Jan. 29, 1946 2,417,924 Gary Mar. 25, 1947 2,515,121 Harsh et a1 July 11, 1950 2,525,532 Dreywood Oct. 10, 1950 FOREIGN PATENTS Number Country Date 813,316 France Jan. 15, 1937 829,757 France Nov. 23, 1937 879,995 France Dec. 10, 1942 OTHER REFERENCES Henney and Dudley: Handbook of Photogra- V phy, Chapter XIII, pp. 378-411, pages particularly cited pp. 395, 396, p. 336, Whittlesley House,

Neblette (Photographic Principles and Practice published by Van Nostrand Co., New York City, pages 559-560).

James and Higgins (Photographic Theory published by John Wiley and Sons, N. Y. 0., pages- 97-99). I 

1. A PHOTOGRAPHIC PROCESS FOR FORMING, BY TRANSFER, A POSITIVE PRINT OF A LATENT IMAGE CONTAINED IN THE SILVER HALIDE EMULSION OF A PHOTOSENSITIVE ELEMENT WHEREIN A SINGLE APPLICATION OF LIQUID TO SAID ELEMENT IS EFFECTIVE TO GIVE A FINISHED PRINT SUFFICIENTLY STABLE TO REQUIRE NO SUBSEQUENT LIQUID STABILIZING TREATMENTS, WHICH PROCESS COMPRISES THE STEPS OF BRINGING A RELATIVELY UNIFORM LAYERWISE DISTRIBUTION OF A PROCESSING LIQUID INTO CONTACT WITH THE PHOTOSENSITIVE ELEMENT SO AS TO PERMEATE SAID EMULSION WITH SAID LIQUID, SAID LAYERWISE DISTRIBUTION OF PROCESSING LIQUID PROVIDING THE ENTIRE MASS OF LIQUID FOR PERFORMING SAID PROCESS; PROVIDING A PRINT-RECEIVING ELEMENT IN SUPERPOSED RELATION WITH THE PHOTOSENSITIVE ELEMENT, SAID PRINT-RECEIVING ELEMENT BEING AT LEAST PARTIALLY PERMEABLE TO THE PROCESSING LIQUID AND THE LAYERWISE DISTRIBUTION OF THE PROCESSING LIQUID BEING CONFINED BETWEEN THE OUTER SURFACES OF SAID SUPERPOSED ELEMENTS THROUGHOUT THE PROCESSING, SAID PROCESSING LIQUID CONTAINING, AFTER PERMEATION OF SAID SILVER HALIDE LAYER, ALL OF THE REAGENT, INCLUDING A SILVER HALIDE DEVELOPER AND AN ALKALI, FOR DEVELOPING THE LATENT IMAGE IN THE SILVER HALIDE EMULSION AND FOR FORMING A POSITIVE PRINT OF THE SUBJECT MATTER OF SAID LATENT IMAGE UPON SAID PRINT-RECEIVING ELEMENT, SAID DEVELOPER BEING CHARACTERIZED BY ITS PROPENSITY FOR OXIDIZING IN AN ALKALINE ENVIRONMENT TO FORM STAINS; AND INTRODUCING INTO THE ALKALINE PROCESSING LIQUID, SUBSEQUENT TO ITS CONTACT WITH THE PHOTOSENSITIVE ELEMENT, A SUBSTANCE OF ACID REACTION IN SUFFICIENT CONCENTRATION TO REDUCE THE ALKALINITY OF SAID PROCESSING LIQUID TO A PH AT WHICH THE UNUSED DEVELOPER THEREIN IS SUBSTANTIALLY INCAPABLE OF OXIDATION TO FORM A STAIN IN SAID POSITIVE PRINT, SAID SUBSTANCE OF ACID REACTION BEING DISSOLVED FROM A PERMEATED PORTION OF ONE OF SAID ELEMENTS AND BEING PRESENT IN SAID PROCESSING LIQUID IN ADDITION TO ALL OF THE REAGENTS FOR FORMING THE TRANSFER PRINT.
 24. A PHOTOGRAPHIC PRODUCT COMPRISING A LIQUID-CONFINING LAYER, INCLUDING AT LEAST A PHOTOSENSITIVE PORTION, SAID PHOTOSENSITIVE PORTION COMPRISING SILVER HALIDE AS THE PHOTOSENSITIVE MATERIAL THEREOF, ANOTHER LIQUID-CONFINING LAYER AND A RUPTURABLE CONTAINER HOLDING A LIQUID, SAID LAYERS AND SAID CONTAINER BEING ASSOCIATED TOGETHER SO AS TO PERMIT SAID LAYERS TO BE SUPERPOSED WITH SAID LIQUID HELD BY SAID CONTAINER POSITO WET SAID LAYERS AND WITH SAID CONTAINER SO AS NOT TIONED FOR RELEASING SAID LIQUID BETWEEN SAID LAYERS, SAID PRODUCT CONTAINING ALL OF THE REAGENTS, INCLUDING A SILVER HALIDE DEVELOPER AND AN ALKALI IN SUFFICIENT QUANTITY TO DEVELOP A LATENT IMAGE IN SAID PHOTOSENSITIVE PORTION AND TO PROVIDE A LAYER OF SAID PRODUCT, OTHER THAN SAID PHOTOSENSITIVE LAYER, WITH A POSITIVE TRANSFER PRINT OF THE SUBJECT MATTER OF SAID LATENT IMAGE, SAID REAGENTS BEING RENDERED EFFECTIVE UPON THE RELEASE OF SAID LIQUID FROM THE RUPTURABLE CONTAINER, SAID SILVER HALIDE DEVELOPER TENDING TO OXIDIZE AND FORM STAINS IN AN ALKALINE ENVIRONMENT, SAID PRODUCT CONTAINING, IN ADDITION TO ALL OF SAID REAGENTS FOR FORMING A TRANSFER PRINT, A SUBSTANCE OF ACID REACTION WHICH IS CARRIED BY ONE OF THE LAYERS OF SAID PRODUCT IN A POSITION TO BE DISSOLVED IN SAID LIQUID UPON THE RELEASE THEREOF, SAID SUBSTANCE OF ACID REACTION BEING OPERATIVE TO REDUCE THE ALKALINITY OF THE LIQUID AT A RATE SUBSTANTIALLY SLOWER THAN THE RATE AT WHICH THE DEVELOPING REACTION TAKES PLACE AND BEING SUFFICIENT IN QUANTITY TO REDUCE THE ALKALINITY OF THE PROCESSING LIQUID TO A PH AT WHICH THE DEVELOPER IS SUBSTANTIALLY INCAPABLE OF OXIDIZING TO FORM STAINS IN SAID POSITIVE TRANSFER PRINT. 